This invention relates generally to the field of container closures, and more particularly to an improved safety type closure or cap adapted to effect a substantially tight seal with respect to the mouth of a container.
As defined by National Formulary, since NF 7, effective from 1942 to 1947, a "well closed" container protects the contents from extraneous solids and from loss of the contents under ordinary or customary conditions of handling, shipment, storage and distribution.
By contrast, a "tight" container protects the contents from contamination by extraneous liquids, solids and vapors, from loss of the drug, and from efflorescence, deliquescence or evaporation under the ordinary or customary conditions of handling, shipment, storage and distribution, and, additionally, is capable of tight reclosure. As a general rule, a tight container must offer moisture permeability some 20 times less than a "well closed" container.
More recently, because of increased standards of safety from the standpoint of discovery and appropriation by children of tender years, container closures have been designed to require knowledgeable manipulation on the part of the user to open the closure, as a result of which recourse to the screw thread type of closure has been severely limited when a "tight" closure is required.
The most common type of safety closure employs a peripheral rim having at least one interrupted segment. A corresponding projection on the cap is rotatably aligned with the interrupted segment during the opening procedure, following which the cap may be lifted at this point to pivot the cap from the container. An example of this type of closure is disclosed in U.S. Pat. No. 3,669,295 of June 13, 1972 to William Horvath. Unlike screw type closures, in which the degree of tightness of the closure depends upon the degree the cap is twisted, snap type caps have a uniform degree of tightness which depends, among other factors, upon the degree of distortion imparted to the synthetic resinous components of the cap, and the elastic modulus of the material from which the cap is made. While it is possible to manufacture threaded type safety caps, including a freely turning outer shell which is engaged with an inner element upon the application of axially directed pressure upon the shell, such constructions are expensive, and require the provision of a resilient jacket of compressible material lining the end wall of the cap.